The present invention relates to high-capacitance microelectronic capacitors, and more particular to an amorphous high dielectric constant thin film material which can be employed as a dielectric in capacitors formed using back-end-of-the-line (BEOL) or damascene technology. The present invention also provides novel integrated circuit (IC) damascene semiconductor devices which comprise a damascene structure and the capacitor of the present invention.
High-capacity IC capacitors, on the order of 1 nF/mm2 or above, connected across the power supply and ground buses of modern microprocessor chips are needed to reduce the power and ground noise to an acceptable level. The high-capacity capacitors should be placed very close to the switching circuits, and be connected to the power and ground buses by a low-resistance conductor. To accomplish this goal, one preferred approach is to build the high-capacity capacitors into the BEOL process.
The dielectric thin film material for such BEOL decoupling capacitors must satisfy both of the following requirements: (1) a high dielectric constant as compared to conventional dielectrics such as SiO2 and Si3N4 (for example, a 100 nm thick film with a dielectric constant of 20 would give a capacitance of 1.8 nF/mm2); and (2) a formation temperature which is compatible with the BEOL metallurgy and processing.
The latter criteria implies that the deposition temperature of the dielectric material used in forming the BEOL decoupling capacitor must be about 450xc2x0 C. or lower. Such a low deposition temperature is required in order to avoid unwanted instability of the BEOL metallurgy used for the power and ground connections.
Although a variety of dielectric materials having high dielectric constants are known in the art, the prior art dielectrics cannot be employed in BEOL processing due to their required high deposition temperatures. An example of such a high dielectric constant material is the crystalline form of certain perovskite-type oxides. Despite having dielectric constants of about 200 or above, crystalline perovskite-type oxides are typically deposited at temperatures of about 500xc2x0 C. or higher, or require a post anneal step using temperatures higher than 500xc2x0 C. As such, the crystalline perovskite-type oxides such as barium strontium titanate (BSTO) cannot be employed in BEOL applications.
In view of the drawbacks mentioned hereinabove concerning prior art dielectric materials, there is a continued need to develop a dielectric material which can be employed in fabricating BEOL decoupling capacitors which meets both of the aforementioned requirements.
One object of the present invention is to provide a thin film dielectric material which can be employed in forming capacitors using the BEOL wiring levels as the capacitor electrodes.
Another object of the present invention is to provide a thin film dielectric material which has a dielectric constant higher than conventional dielectric materials such as SiO2 (xcex5≅4.0), Si3N4 (xcex5≅7.0) and Al2O3 (xcex5≅9.0) and which can also be formed at temperatures that are compatible with the BEOL metallurgy.
A further object of the present invention is to provide a high-capacity BEOL decoupling capacitor which has a capacity on the order of 2 nF/mm2 or above.
A still further object of the present invention is to provide a thin film dielectric material which exhibits good conformality to the electrode structure and geometry to which it is applied as well as a low leakage current that is on the order of 1 xcexcA/cm2 or less.
A yet further object of the present invention is to provide high capacitance capacitors to damascene structures which exhibit low leakage current.
These and other objects and advantages are achieved in the present invention by utilizing an amorphous perovskite-type oxide as a thin film dielectric material. Specifically, the present invention relates to high-capacitance capacitors formed using thin film materials which are in the amorphous phase as the dielectric material in capacitors formed using the BEOL wiring levels as the capacitor electrodes in the integrated-circuit chip. These wiring levels include the power and ground levels. As such, the capacitors can be placed in close proximity to the switching circuits and provide effective filtering and noise reduction.
At the BEOL level, ambient temperatures must be kept low, less than about 450xc2x0 C., thus the novel capacitors of this invention use a low temperature deposition and annealing process to stay at or below this temperature. This ensures formation of a dielectric material which is in the amorphous phase. It has been determined that the amorphous phase of barium strontium titanate (BSTO) has a dielectric constant of up to about 25 or more which value is significantly higher than that of the typical dielectrics used in circuit applications. Other perovskite-type oxides such as lead lanthanum titanate (PLTO), barium zirconium titanate (BZTO) and tantalum titanate (TTO) can have even greater dielectric constants in their amorphous phase. Capacitors formed utilizing these particular types of amorphous dielectrics also exhibit low leakage and good conformality.
In another aspect of the present invention, the capacitors of the present invention are used in fabricating novel IC damascene semiconductor devices. In this embodiment, the capacitor can be fabricated on the outermost wiring level of the damascene structure, on wiring levels beneath the outermost wiring level, or in a trench which is formed in the interlevel dielectric of the damascene structure.